Stability of cortical responses and the statistics of natural scenes.

The primary visual cortex (V1) of higher mammals contains maps of stimulus features; how these maps influence vision remains unknown. We have examined the functional significance of an asymmetry in the orientation map in cat V1, i.e., the fact that a larger area of V1 is preferentially activated by vertical and horizontal contours than by contours at oblique orientations. Despite the fact that neurons tuned to cardinal and oblique orientations have indistinguishable tuning characteristics, cardinal neurons remain more stable in their response properties after selective perturbation induced by adaptation. Similarly, human observers report different adaptation-induced changes in orientation tuning between cardinal and oblique axes. We suggest that the larger cortical area devoted to cardinal orientations imposes stability on the processing of cardinal contours during visual perception, by retaining invariant cortical responses along cardinal axes.     

Expansion of direction space around the cardinal axes revealed by smooth pursuit eye movements

It is well established that perceptual direction discrimination shows an oblique effect; thresholds are higher for motion along diagonal directions than for motion along cardinal directions. Here, we compare simultaneous direction judgments and pursuit responses for the same motion stimuli and find that both pursuit and perceptual thresholds show similar anisotropies. The pursuit oblique effect is robust under a wide range of experimental manipulations, being largely resistant to changes in trajectory (radial versus tangential motion), speed (10 versus 25 deg/s), directional uncertainty (blocked versus randomly interleaved), and cognitive state (tracking alone versus concurrent tracking and perceptual tasks). Our data show that the pursuit oblique effect is caused by an effective expansion of direction space surrounding the cardinal directions and the requisite compression of space for other directions. This expansion suggests that the directions around the cardinal directions are in some way overrepresented in the visual cortical pathways that drive both smooth pursuit and perception.     

Beliefs about the Minds of Others Influence How We Process Sensory Information

Attending where others gaze is one of the most fundamental mechanisms of social cognition. The present study is the first to examine the impact of the attribution of mind to others on gaze-guided attentional orienting and its ERP correlates. Using a paradigm in which attention was guided to a location by the gaze of a centrally presented face, we manipulated participants'' beliefs about the gazer: gaze behavior was believed to result either from operations of a mind or from a machine. In Experiment 1, beliefs were manipulated by cue identity (human or robot), while in Experiment 2, cue identity (robot) remained identical across conditions and beliefs were manipulated solely via instruction, which was irrelevant to the task. ERP results and behavior showed that participants'' attention was guided by gaze only when gaze was believed to be controlled by a human. Specifically, the P1 was more enhanced for validly, relative to invalidly, cued targets only when participants believed the gaze behavior was the result of a mind, rather than of a machine. This shows that sensory gain control can be influenced by higher-order (task-irrelevant) beliefs about the observed scene. We propose a new interdisciplinary model of social attention, which integrates ideas from cognitive and social neuroscience, as well as philosophy in order to provide a framework for understanding a crucial aspect of how humans'' beliefs about the observed scene influence sensory processing.     

Separate coding of different gaze directions in the superior temporal sulcus and inferior parietal lobule

Electrophysiological recording in the anterior superior temporal sulcus (STS) of monkeys has demonstrated separate cell populations responsive to direct and averted gaze. Human functional imaging has demonstrated posterior STS activation in gaze processing, particularly in coding the intentions conveyed by gaze, but to date has provided no evidence of dissociable coding of different gaze directions. Because the spatial resolution typical of group-based fMRI studies (approximately 6-10 mm) exceeds the size of cellular patches sensitive to different facial characteristics (1-4 mm in monkeys), a more sensitive technique may be required. We therefore used fMRI adaptation, which is considered to offer superior resolution, to investigate whether the human anterior STS contains representations of different gaze directions, as suggested by non-human primate research. Subjects viewed probe faces gazing left, directly ahead, or right. Adapting to leftward gaze produced a reduction in BOLD response to left relative to right (and direct) gaze probes in the anterior STS and inferior parietal cortex; rightward gaze adaptation produced a corresponding reduction to right gaze probes. Consistent with these findings, averted gaze in the adapted direction was misidentified as direct. Our study provides the first human evidence of dissociable neural systems for left and right gaze.     

Testing Neuronal Accounts of Anisotropic Motion Perception with Computational Modelling

There is an over-representation of neurons in early visual cortical areas that respond most strongly to cardinal (horizontal and vertical) orientations and directions of visual stimuli, and cardinal- and oblique-preferring neurons are reported to have different tuning curves. Collectively, these neuronal anisotropies can explain two commonly-reported phenomena of motion perception – the oblique effect and reference repulsion – but it remains unclear whether neuronal anisotropies can simultaneously account for both perceptual effects. We show in psychophysical experiments that reference repulsion and the oblique effect do not depend on the duration of a moving stimulus, and that brief adaptation to a single direction simultaneously causes a reference repulsion in the orientation domain, and the inverse of the oblique effect in the direction domain. We attempted to link these results to underlying neuronal anisotropies by implementing a large family of neuronal decoding models with parametrically varied levels of anisotropy in neuronal direction-tuning preferences, tuning bandwidths and spiking rates. Surprisingly, no model instantiation was able to satisfactorily explain our perceptual data. We argue that the oblique effect arises from the anisotropic distribution of preferred directions evident in V1 and MT, but that reference repulsion occurs separately, perhaps reflecting a process of categorisation occurring in higher-order cortical areas.     

A computational analysis of separating motion signals in transparent random dot kinematograms

When multiple motion directions are presented simultaneously within the same region of the visual field human observers see motion transparency. This perceptual phenomenon requires from the visual system to separate different motion signal distributions, which are characterised by distinct means that correspond to the different dot directions and variances that are determined by the signal and processing noise. Averaging of local motion signals can be employed to reduce noise components, but such pooling could at the same time lead to the averaging of different directional signal components, arising from spatially adjacent dots moving in different directions, which would reduce the visibility of transparent directions. To study the theoretical limitations of encoding transparent motion by a biologically plausible motion detector network, the distributions of motion directions signalled by a motion detector model (2DMD) were analysed here for Random Dot Kinematograms (RDKs). In sparse dot RDKs with two randomly interleaved motion directions, the angular separation that still allows us to separate two directions is limited by the internal noise in the system. Under the present conditions direction differences down to 30 deg could be separated. Correspondingly, in a transparent motion stimulus containing multiple motion directions, more than eight directions could be separated. When this computational analysis is compared to some published psychophysical data, it appears that the experimental results do not reach the predicted limits. Whereas the computer simulations demonstrate that even an unsophisticated motion detector network would be appropriate to represent a considerable number of motion directions simultaneously within the same region, human observers usually are restricted to seeing not more than two or three directions under comparable conditions. This raises the question why human observers do not make full use of information that could be easily extracted from the representation of motion signals at the early stages of the visual system.     

Categorical perception of orientation in monkeys

Structural and functional substrates of orientation processing in monkeys have been clarified. However, orientation perception in monkeys has not been fully studied. In this study, the cognitive mechanism that controls monkeys' perception of orientation was evaluated. After the monkeys were trained to discriminate between a cardinal and an oblique orientation (e.g., 0 degrees and 30 degrees), their perceptual mechanisms underlying orientation discrimination were tested by using six orientations, ranging from 0 degrees to 150 degrees, including ones used in the discrimination training. Generalization tests showed that the monkeys who were trained with cardinal orientations (e.g., 0 degrees) as positive stimuli generalized their responses to the other cardinal orientation (e.g., 90 degrees). Similarly, the monkeys who were trained with oblique orientations (e.g., 30 degrees) as positive stimuli generalized their responses to all other oblique orientations (e.g., 60 degrees, 120 degrees, and 150 degrees). These findings indicated that the monkeys abstracted the quality of the cardinal/oblique category from the physical features of orientation stimuli although they were not trained to do so. Such an abstraction also suggested a discrepancy between a continuously and orderly arranged cortical map and a discontinuously categorized perception of orientation. The present findings provide insight into the learning-correlated plasticity of cortical orientation preference.     

The role of observers' gaze behaviour when watching object manipulation tasks: predicting and evaluating the consequences of action

When watching an actor manipulate objects, observers, like the actor, naturally direct their gaze to each object as the hand approaches and typically maintain gaze on the object until the hand departs. Here, we probed the function of observers'' eye movements, focusing on two possibilities: (i) that observers'' gaze behaviour arises from processes involved in the prediction of the target object of the actor''s reaching movement and (ii) that this gaze behaviour supports the evaluation of mechanical events that arise from interactions between the actor''s hand and objects. Observers watched an actor reach for and lift one of two presented objects. The observers'' task was either to predict the target object or judge its weight. Proactive gaze behaviour, similar to that seen in self-guided action–observation, was seen in the weight judgement task, which requires evaluating mechanical events associated with lifting, but not in the target prediction task. We submit that an important function of gaze behaviour in self-guided action observation is the evaluation of mechanical events associated with interactions between the hand and object. By comparing predicted and actual mechanical events, observers, like actors, can gain knowledge about the world, including information about objects they may subsequently act upon.     

Temporal Learning and List-Level Proportion Congruency: Conflict Adaptation or Learning When to Respond?

The current report presents a temporal learning account as a potential alternative to the conflict adaptation account of list-level proportion congruent effects in the Stroop paradigm. Specifically, retrieval of information about response times on previous trials influences a participant''s preparedness to respond at a similar time on following trials. First, an adaptation of the Parallel Episodic Processing (PEP) model is presented, and a list-level effect is produced with a temporal learning mechanism. Next, linear mixed effect model analyses show that temporal learning biases are present in list-level proportion congruent data. A non-conflict experiment is then presented in which a list-level effect is observed with a contrast, rather than congruency, manipulation. Analyses of the experimental and simulated data could not, however, provide a clear picture of whether temporal learning was the sole contributor to the list-level proportion congruent effect. These results do, however, demonstrate that caution is warranted when interpreting list-level proportion congruent effects.     

Anisotropies in peripheral vernier acuity

Vernier acuity for short horizontal, vertical and oblique target lines was measured in many locations in the periphery of the visual field in normal human observers. In the 10 deg periphery, the average alignment threshold with oblique vernier lines in eight locations for three observers was 2.29 times higher than that with vertical and horizontal target lines. This oblique effect was found everywhere in the visual field. Similar conclusions are drawn for configurations in which the lines were replaced by just their distal endpoints, but here, additionally, performance was distinctly better when the dot pair was collinear with the fixation point, i.e. oriented radially, than when it was oriented tangentially. Both for vernier lines and for dot pairs, in all observers, horizontal configurations showed somewhat better thresholds than vertical ones. These results suggest an inherent pattern of connectivity throughout the visual field favoring processing in the cardinal orientations over the obliques, the radial over the tangential and, to a limited extent, the horizontal over the vertical.     

Pictorial gaze cues do not enhance long-tailed macaques' performance on a computerised object-location task

The perception of pictorial gaze cues was examined in long-tailed macaques (Macaca fascicularis). A computerised object-location task was used to explore whether the monkeys would show faster response time to locate a target when its appearance was preceded with congruent as opposed to incongruent gaze cues. Despite existing evidence that macaques preferentially attend to the eyes in facial images and also visually orient with depicted gaze cues, the monkeys did not show faster response times on congruent trials either in response to schematic or photographic stimuli. These findings coincide with those reported for baboons testing with a similar paradigm in which gaze cues preceded a target identification task [Fagot, J., Deruelle, C., 2002. Perception of pictorial gaze by baboons (Papio papio). J. Exp. Psychol. 28, 298-308]. When tested with either pictorial stimuli or interactants, nonhuman primates readily follow gaze but do not seem to use this mechanism to identify a target object; there seems to be some mismatch in performance between attentional changes and manual responses to gaze cues on ostensibly similar tasks.     

Attention in natural scenes: contrast affects rapid visual processing and fixations alike

For natural scenes, attention is frequently quantified either by performance during rapid presentation or by gaze allocation during prolonged viewing. Both paradigms operate on different time scales, and tap into covert and overt attention, respectively. To compare these, we ask some observers to detect targets (animals/vehicles) in rapid sequences, and others to freely view the same target images for 3 s, while their gaze is tracked. In some stimuli, the target''s contrast is modified (increased/decreased) and its background modified either in the same or in the opposite way. We find that increasing target contrast relative to the background increases fixations and detection alike, whereas decreasing target contrast and simultaneously increasing background contrast has little effect. Contrast increase for the whole image (target + background) improves detection, decrease worsens detection, whereas fixation probability remains unaffected by whole-image modifications. Object-unrelated local increase or decrease of contrast attracts gaze, but less than actual objects, supporting a precedence of objects over low-level features. Detection and fixation probability are correlated: the more likely a target is detected in one paradigm, the more likely it is fixated in the other. Hence, the link between overt and covert attention, which has been established in simple stimuli, transfers to more naturalistic scenarios.     

“Community Work” in a Climate of Adaptation: Responding to Change in Rural Alaska

We draw on our research experiences with municipal workers in Alaska, where the impacts of climate change are already extensive, to examine adaptation and related concepts, such as resilience and vulnerability, which have become widely used in science and policy formulation for addressing climate change despite also being subject to multiple critiques. We use local people’s experiences with environmental challenges to illustrate limitations of the climate change adaptation paradigm, and offer the additional concept of “community work” — analogous to niche construction — as a counterpart to the adaptive process at the community level. Whereas climate change adaptation insinuates active and purposive change, the reality we have repeatedly encountered is that people in these communities focus not on changing but on building and maintaining capacity and achieving stability: keeping aging and overtaxed infrastructure running while also working toward improving quality of life and services in their communities. We discuss how these findings are congruent with recent calls to better situate climate change adaptation policy in the context of community development, and argue that scientists and policymakers need to understand this context of community work to avoid the pitfalls that potentially accompany the adaptation paradigm.     

Decoupled Visually-Guided Reaching in Optic Ataxia: Differences in Motor Control between Canonical and Non-Canonical Orientations in Space

Guiding a limb often involves situations in which the spatial location of the target for gaze and limb movement are not congruent (i.e. have been decoupled). Such decoupled situations involve both the implementation of a cognitive rule (i.e. strategic control) and the online monitoring of the limb position relative to gaze and target (i.e. sensorimotor recalibration). To further understand the neural mechanisms underlying these different types of visuomotor control, we tested patient IG who has bilateral caudal superior parietal lobule (SPL) damage resulting in optic ataxia (OA), and compared her performance with six age-matched controls on a series of center-out reaching tasks. The tasks comprised 1) directing a cursor that had been rotated (180° or 90°) within the same spatial plane as the visual display, or 2) moving the hand along a different spatial plane than the visual display (horizontal or para-sagittal). Importantly, all conditions were performed towards visual targets located along either the horizontal axis (left and right; which can be guided from strategic control) or the diagonal axes (top-left and top-right; which require on-line trajectory elaboration and updating by sensorimotor recalibration). The bilateral OA patient performed much better in decoupled visuomotor control towards the horizontal targets, a canonical situation in which well-categorized allocentric cues could be utilized (i.e. guiding cursor direction perpendicular to computer monitor border). Relative to neurologically intact adults, IG''s performance suffered towards diagonal targets, a non-canonical situation in which only less-categorized allocentric cues were available (i.e. guiding cursor direction at an off-axis angle to computer monitor border), and she was therefore required to rely on sensorimotor recalibration of her decoupled limb. We propose that an intact caudal SPL is crucial for any decoupled visuomotor control, particularly when relying on the realignment between vision and proprioception without reliable allocentric cues towards non-canonical orientations in space.     

I See What You Mean: How Attentional Selection Is Shaped by Ascribing Intentions to Others

The ability to understand and predict others’ behavior is essential for successful interactions. When making predictions about what other humans will do, we treat them as intentional systems and adopt the intentional stance, i.e., refer to their mental states such as desires and intentions. In the present experiments, we investigated whether the mere belief that the observed agent is an intentional system influences basic social attention mechanisms. We presented pictures of a human and a robot face in a gaze cuing paradigm and manipulated the likelihood of adopting the intentional stance by instruction: in some conditions, participants were told that they were observing a human or a robot, in others, that they were observing a human-like mannequin or a robot whose eyes were controlled by a human. In conditions in which participants were made to believe they were observing human behavior (intentional stance likely) gaze cuing effects were significantly larger as compared to conditions when adopting the intentional stance was less likely. This effect was independent of whether a human or a robot face was presented. Therefore, we conclude that adopting the intentional stance when observing others’ behavior fundamentally influences basic mechanisms of social attention. The present results provide striking evidence that high-level cognitive processes, such as beliefs, modulate bottom-up mechanisms of attentional selection in a top-down manner.     

Do American Crows Pay Attention to Human Gaze and Facial Expressions?

Interactions between species can lead to the evolution of interspecific communication. Non‐verbal communication by humans, both intentional and unintentional, can be interpreted by other species. We tested whether American crows (Corvus brachyrhynchos) were sensitive to human facial features under field conditions by comparing flight initiation distances and urgency of escape behavior to human approaches varying in eye contact and facial expression. We first examined whether crows distinguish between an approaching human who is directly gazing at them and a human approaching them with an averted gaze. In a second experiment, we tested whether crows differentiate a smiling from scowling human approaching them with direct or averted gaze. In the first experiment, we found that crows fled sooner and more urgently when humans were directly gazing at them. Similarly, in the second experiment, crows responded sooner to a direct vs. averted gaze; however, they did not react differently to varying human facial expressions. We suggest that crows use human gaze as a reliable visual cue compared with facial expressions when making decisions about responding to approaching humans. This is the first study to show that a wild corvid species changes its behavior based on human gaze, possibly representing an adaptation to living in human‐dominated urban areas and suggesting crows might perceive human intention by this visual cue.     

Extra-retinal adaptation of cortical motion-processing areas during pursuit eye movements

Repetitive eye movement produces a compelling motion aftereffect (MAE). One mechanism thought to contribute to the illusory movement is an extra-retinal motion signal generated after adaptation. However, extra-retinal signals are also generated during pursuit. They modulate activity within cortical motion-processing area MST, helping transform retinal motion into motion in the world during an eye movement. Given the evidence that MST plays a key role in generating MAE, it may also become indirectly adapted by prolonged pursuit. To differentiate between these two extra-retinal mechanisms we examined storage of the MAE across a period of darkness. In one condition observers were told to stare at a moving pattern, an instruction that induces a more reflexive type of eye movement. In another they were told to deliberately pursue it. We found equally long MAEs when testing immediately after adaptation but not when the test was delayed by 40 s. In the case of the reflexive eye movement the delay almost completely extinguished the MAE, whereas the illusory motion following pursuit remained intact. This suggests pursuit adapts cortical motion-processing areas whereas unintentional eye movement does not. A second experiment showed that cortical mechanisms cannot be the sole determinant of pursuit-induced MAE. Following oblique pursuit, we found MAE direction changes from oblique to vertical. Perceived MAE direction appears to be influenced by a subcortical mechanism as well, one based on the relative recovery rate of horizontal and vertical eye-movement processes recruited during oblique pursuit.     

Transfer of tilt after-effects between second-order cues

Second-order cues are visual stimuli that are detectable by human observers, without eliciting a peak in Fourier energy that corresponds to their perceptual properties. The most commonly studied exemplars of second-order cues are those defined by modulation of local contrast (CM). It is widely accepted that such cues are initially detected separately from first-order, luminance modulated (LM), cues. However, after-effects have been shown to transfer between first- and second-order cues (LM and CM, respectively). This suggests the existence of a late link in the mechanisms that subserve their processing. To extend the investigation of the mechanisms for processing second-order cues we consider cues defined by modulations in local orientation (OM). Using a tilt-after-effect (TAE) paradigm, we found partial transfer of adaptation between LM and OM cues, confirming the presence of a link between first and second-order cues. Furthermore, we found a partial transfer of TAE between OM and CM cues. These results suggest that, at or before the site of adaptation, information from all visual cues is combined. However, as transfer of adaptation is below 100% in all cases, this is only a partial integration of information.     

Fear is readily associated with an out-group face in a minimal group context

Research on prepared learning demonstrates that fear-conditioning biases may exist to natural hazards (e.g., snakes) compared to nonnatural hazards (e.g., electrical cords) and that fear is more readily learned toward exemplars of a racial out-group than toward exemplars of one's own race. Here we push the limits of the generalizability of the mechanisms underlying race biases in a fear-conditioning paradigm by using arbitrary group categories not distinguished by race. Groups were distinguishable solely by t-shirt color, with assignment based on performance in a perceptual task. In this “minimal group paradigm,” we found that out-group exemplars were more readily associated with an aversive stimulus than exemplars of one's in-group. Our findings suggest that prepared learning in an intergroup context is not limited to contexts involving racial categories involving histories rife with cultural stereotypes and that previous findings of learning biases along racial lines may be interpreted as a by-product of a broader psychological system for prepared fear learning toward categories of agents that may have posed persistent threats over human evolutionary history.